U.S. patent application number 10/818811 was filed with the patent office on 2004-11-25 for electrostatic discharge protection component.
Invention is credited to Inoue, Tatsuya, Orita, Takeshi, Tokunaga, Hideaki, Uriu, Eiichi, Yoneda, Naotsugu.
Application Number | 20040233606 10/818811 |
Document ID | / |
Family ID | 33447047 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040233606 |
Kind Code |
A1 |
Inoue, Tatsuya ; et
al. |
November 25, 2004 |
Electrostatic discharge protection component
Abstract
On the surface of a ceramic sinter, at least an external
electrode for input, an external electrode for output, and external
electrodes for grounding are disposed, and the ceramic sinter
includes an inductor electrically connected to the external
electrode for input and external electrode for output, and a
varistor electrically connected to the external electrode for input
and external electrodes for grounding. By connecting the inductor
to the signal line of the circuit of an electronic appliance and
connecting the varistor between the input side of the signal line
and the ground, electrostatic discharge pulses of about 0.5 to 2
nanoseconds can be suppressed efficiently.
Inventors: |
Inoue, Tatsuya;
(Takatsuki-shi, JP) ; Tokunaga, Hideaki;
(Fukui-shi, JP) ; Uriu, Eiichi; (Hirakata-shi,
JP) ; Yoneda, Naotsugu; (Katano-shi, JP) ;
Orita, Takeshi; (Neyagawa-shi, JP) |
Correspondence
Address: |
LAWRENCE E. ASHERY
SUITE 301
ONE WESTLAKES, BERWYN
P.O. BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
33447047 |
Appl. No.: |
10/818811 |
Filed: |
April 6, 2004 |
Current U.S.
Class: |
361/118 |
Current CPC
Class: |
H02H 9/04 20130101; H01C
7/12 20130101; H01C 1/16 20130101; H02H 9/044 20130101; H01F
17/0013 20130101; H01C 7/102 20130101 |
Class at
Publication: |
361/118 |
International
Class: |
H02H 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2003 |
JP |
2003-106406 |
Claims
What is claimed is:
1. An electrostatic discharge protection component comprising a
ceramic sinter, and an external electrode for input, an external
electrode for output, and external electrodes for grounding formed
on a surface including the ends of the ceramic sinter, said ceramic
sinter including: one or more inductors electrically connecting the
external electrode for input and the external electrode for output,
and one or more varistors electrically connecting the external
electrode for input and the external electrodes for grounding.
2. The electrostatic discharge protection component of claim 1,
wherein said inductor has an impedance of 200 .OMEGA. or more in
frequency band of measuring frequency of 300 MHz to 800 MHz.
3. The electrostatic discharge protection component of claim 1,
wherein said ceramic sinter further includes a second varistor for
electrically connecting the external electrode for output and the
external electrodes for grounding.
4. The electrostatic discharge protection component of claim 1,
wherein a plurality of inductors are disposed in series between the
external electrode for input and the external electrode for output,
and a varistor is further disposed for electrically connecting the
external electrode for output and the external electrodes for
grounding, and a varistor is also disposed for electrically
connecting to the plurality of inductors and the external
electrodes for grounding.
5. The electrostatic discharge protection component of claim 1,
wherein plural sets of the external electrode for input and the
external electrode for output are provided, an inductor is disposed
for electrically connecting to the plurality of the external
electrodes for input and the external electrodes for output, and a
varistor is disposed for electrically connecting to the external
electrodes for input and the external electrodes for grounding.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an electrostatic discharge
protection component (hereinafter referred to simply as protection
component) used for protecting an electronic appliance from
electrostatic discharge.
BACKGROUND OF THE INVENTION
[0002] In rapid progress of trend of smaller size and higher
performance of electronic appliances such as cellphones, recently,
the withstand voltage of the electronic components used in the
electronic appliances tends to be lower. Accordingly, there is an
increasing number of breakdown accidents of electric circuits
inside the appliance due to electrostatic discharge pulse caused by
contact between part of human body and terminal of electronic
appliance. When electrostatic discharge is generated, a high
voltage of a bout hundreds of volts to several kilovolts is
generated and applied to the electronic appliance in a scant moment
of 0.5 to 2 nanoseconds.
[0003] Hitherto, as measure against such electrostatic discharge
pulse, it has been proposed to bypass the electrostatic discharge
by disposing a varistor or zener diode between the incoming line of
electrostatic discharge and the ground, and to suppress the voltage
applied to the electric circuit of the appliance.
[0004] Moreover, as disclosed in Japanese Laid-open Patent No.
S63-56023, in a satellite broadcast receiving apparatus comprising
a plane antenna for satellite broadcast not grounded in direct
current, and a converter connected to the plane antenna by way of a
transmission line having an amplifying circuit in a front stage, a
filter circuit composed of an inductive element for connecting the
transmission line and the ground, and a capacitive element
connected to a rear stage of the connection point of the inductive
element and transmission line is provided between the plane antenna
and the amplifying circuit, thereby preventing damage by
electrostatic discharge. An air gap coil is used as the inductive
element, and a capacitor is used as the capacitive element.
[0005] However, if attempted to suppress the voltage applied to the
electric circuit of the appliance by bypassing the electrostatic
discharge by using the varistor or zener diode or in the disclosed
method, since the reaction speed of the elements such as varistor
or zener diode to the electrostatic discharge pulse is slow,
sufficient bypassing effect is not obtained. Although somewhat
different depending on the size or composition of the elements,
electrostatic discharge occurring in about 0.5 to 2 nanoseconds
cannot be bypassed sufficiently. Therefore, existing protection
components cannot suppress sufficiently the highest peak voltage in
about 0.5 to 2 nanoseconds occurring as electrostatic discharge,
and it has been difficult to prevent breakdown of electronic
components or electronic appliances securely. However, when a
varistor or zener diode of very high capacity such as several nF
unit or more is used, peak voltage of about 0.5 to 2 nanoseconds
may be suppressed to a certain extent. But such element cannot be
used in a high speed transmission circuit of more than tens of MHz
units.
SUMMARY OF THE INVENTION
[0006] The invention is devised in the light of the above problems,
and it is hence an object thereof to present a protection component
capable of suppressing pulse peak voltage of about 0.5 to 2
nanoseconds generated by electrostatic discharge.
[0007] To achieve the object, the protection component of the
invention comprises:
[0008] at least three external electrodes for input, output and
grounding disposed on the surface of a ceramic sinter,
[0009] the ceramic sinter includes:
[0010] an inductor electrically connected the external electrode
for input and the external electrode for output, and
[0011] a varistor electrically connected the external electrode for
input and the external electrode for grounding.
[0012] In this configuration, in a signal line of circuit of
electronic appliance, an inductor of the protection component is
connected, and the varistor is connected between the input side of
the signal line and the grounding side, and thereby electrostatic
discharge pulse can be prevented effectively. That is, the inductor
connected in series to the signal line becomes relatively high in
impedance against the high frequency components in the leading
section of electrostatic discharge pulse. Accordingly, the inductor
suppresses passing of electrostatic discharge pulse to the signal
line, and the varistor characteristic is dominant, thereby
bypassing to the grounding side in a short time by the varistor,
and the voltage applied to the protected circuit is substantially
decreased. As a result, it can suppress the peak voltage of about
0.5 to 2 nanoseconds of electrostatic discharge pulse not
controlled sufficiently by the conventional protection component,
and application of electrostatic discharge pulse to the circuit of
electronic appliance can be prevented. Moreover, since the inductor
is disposed in series to the signal line and the varistor is
disposed parallel in L-configuration, the inductance of the
inductor and the capacitance of the varistor may be combined to
function as a low pass filter (noise filter). Thus, two functions
are realized at the same time, and by using one component only, the
size of the appliance can be reduced, and the mounting cost is also
lowered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an outline perspective view of protection
component in exemplary embodiment 1 of the invention.
[0014] FIG. 2 is a schematic perspective exploded view of ceramic
sinter for composing the protection component in the exemplary
embodiment.
[0015] FIG. 3 is an equivalent circuit diagram of the protection
component.
[0016] FIG. 4 is a diagram showing results of measurement of
frequency characteristic of impedance of the protection
component.
[0017] FIG. 5 is a circuit diagram of electrostatic discharge test
in the exemplary embodiment.
[0018] FIG. 6 is a voltage waveform diagram when 8 kV is applied as
electrostatic discharge pulse in the absence of evaluation sample
in electrostatic discharge test circuit in the exemplary
embodiment.
[0019] FIG. 7 is a diagram of voltage waveform applied to the
protected appliance when a conventional laminated varistor is
connected between signal line and grounding line.
[0020] FIG. 8 is a diagram of voltage waveform applied to the
protected appliance furnished with the protection component with
inductance of 68 nH in the exemplary embodiment.
[0021] FIG. 9 is a diagram of voltage waveform applied to the
protected appliance furnished with the protection component with
inductance of 220 nH in the exemplary embodiment.
[0022] FIG. 10 is a schematic perspective exploded view of ceramic
sinter for composing a protection component in exemplary embodiment
2 of the invention.
[0023] FIG. 11 is an equivalent circuit diagram of the protection
component in the exemplary embodiment.
[0024] FIG. 12 is a diagram of voltage waveform applied to the
protected appliance furnished with the protection component in the
exemplary embodiment.
[0025] FIG. 13 is a diagram of voltage waveform applied to the
protected appliance furnished with the protection component of
exemplary embodiment 1 with inductance of 220 nH connected
reversely in the exemplary embodiment.
[0026] FIG. 14 is a schematic perspective exploded view of ceramic
sinter for composing a protection component in exemplary embodiment
3 of the invention.
[0027] FIG. 15 is an equivalent circuit diagram of the protection
component in the exemplary embodiment.
[0028] FIG. 16 is a diagram of voltage waveform applied to the
protected appliance furnished with the protection component in the
exemplary embodiment.
[0029] FIG. 17 is an outline perspective view of a protection
component in exemplary embodiment 4 of the invention.
[0030] FIG. 18 is a schematic perspective exploded view of ceramic
sinter for composing the protection component in the exemplary
embodiment.
[0031] FIG. 19 is an equivalent circuit diagram of the protection
component in the exemplary embodiment.
[0032] FIG. 20 is a diagram showing results of measurement of
frequency characteristic of impedance of the protection component
in the exemplary embodiment.
[0033] FIG. 21 is a diagram of voltage waveform applied to the
protected appliance furnished with the protection component in the
exemplary embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Referring now to the drawings, exemplary embodiments of the
invention are described below. Same elements are identified with
same reference numerals, and duplicate explanation may be
omitted.
FIRST EXEMPLARY EMBODIMENT
[0035] FIG. 1 is an outline perspective view of a protection
component in exemplary embodiment 1 of the invention, and FIG. 2 is
a schematic perspective exploded view of ceramic sinter for
composing this protection component. FIG. 3 is an equivalent
circuit diagram of the protection component.
[0036] The protection component of the invention comprises an
external electrode for input 301 and an external electrode for
output 302 disposed at both shorter sides of a ceramic sinter 25,
and external electrodes for grounding 31 disposed at both longer
sides. The internal structure of the ceramic sinter 25 is shown in
FIG. 2. The ceramic sinter 25 is an integrated laminated body of
varistor 22, inductor 21, and cover layers 231, 232 as surface
protective layers.
[0037] The inductor 21 includes a wiring conductor 12 formed in a
ceramic layer 10, and a via conductor 13 filling up a via (not
shown) opened in the ceramic layer 10, which are connected together
to form a spiral coil conductor 11, and ends 121, 122 of the coil
conductor 11 are drawn out to both shorter sides of the ceramic
sinter 25. In FIG. 2, the wiring conductor 12 is formed on seven
ceramic layers 10, and connected by the via conductor 13 formed in
six vias, and the coil conductor 11 of 3.5 turns is formed.
[0038] The varistor 22 is formed by laminating the ceramic layer
10, and first internal electrode 141 and second internal electrode
142 different in shape formed on the ceramic layer 10, alternately
in four layers, and the end of the first internal electrode 141 is
drawn out to the shorter side of the ceramic sinter 25, and the end
of the second internal electrode 142 is drawn out to both longer
sides. As known from the diagram, the first internal electrode 141
contacts with one shorter side of the ceramic sinter 25, but is
deviated so as not to contact with other shorter side. The second
internal electrode 142 contacts with both longer sides. The first
internal electrode 141 and second internal electrode 142 are
laminated alternately on the ceramic layer 10. However, FIG. 2 is a
schematic diagram, and the number of layers of lamination varies
with the required inductance value or capacitance value.
[0039] At one shorter side of the ceramic sinter 25 having such
internal structure, the external electrode for input 301
electrically connected to one end 122 of the coil conductor 11 and
the end of the first internal electrode 141 is formed. At other
shorter side of the ceramic sinter 25, the external electrode for
output 302 electrically connected to other end 121 of the coil
conductor 11 is formed. Further, in the middle of both longer sides
of the ceramic sinter 25, the external electrode for grounding 31
electrically connected to the second internal electrode 142 is
formed. Thus, the external electrode for input 301, external
electrode for output 302, and external electrode for grounding 31
are formed ion the ceramic sinter 25, and the protection component
of the exemplary embodiment is composed.
[0040] That is, the protection component of the exemplary
embodiment is an integral structure of inductor and varistor formed
in the ceramic sinter 25. The end 122 of the inductor 21 is
connected to the external electrode for input 301, and other end
121 is connected to the external electrode for output 302,
electrically. In the varistor 22, the end of the first internal
electrode 141 is connected to the external electrode for input 301,
and the end of the second internal electrode 142 is connected to
the external electrode for grounding 31, electrically.
[0041] FIG. 3 is an equivalent circuit diagram of the protection
component of the exemplary embodiment. In FIG. 3, a varistor 201
corresponds to the varistor 22 of the ceramic sinter 25, and an
inductor 202 corresponds to the inductor 21 of the ceramic sinter
25. Similarly, an external electrode for input 203, an external
electrode for output 204, and an external electrode for grounding
205 correspond to the external electrode for input 301, external
electrode for output 302, and external electrode for grounding 31
in FIG. 1, respectively.
[0042] In this exemplary embodiment, on the basis of the shape
shown in FIG. 1, the region of forming the external electrode for
input 301 and external electrode for output 302 forms shorter
sides, but these external electrodes may not be always formed at
the shorter sides. That is, depending on the internal structure,
the external electrode for input 301 and external electrode for
output 302 may be formed at the longer sides, and the external
electrodes for grounding 31 may be formed at the shorter sides.
[0043] A manufacturing method of the protection component in the
exemplary embodiment is explained below while referring to FIG. 1
and FIG. 2.
[0044] First of all, a green sheet of zinc oxide is fabricated by
using ceramic powder mainly composed of zinc oxide and an organic
binder. At this time, the thickness of the green sheet is about 50
.mu.m. In this exemplary embodiment, after sintering the zinc oxide
green sheet, a ceramic layer 10 is obtained, and hence the ceramic
layer 10 is hereinafter referred to as zinc oxide green sheet 10.
The internal electrode and wiring conductor are expressed the same
before and after baking.
[0045] Consequently, a plurality of zinc oxide green sheets 10 are
laminated, and a lower side cover layer 231 is formed. In FIG. 2,
two cover layers 231 are shown. In succession, similar zinc oxide
green sheets 10 are laminated on the cover layer 231, and a metal
paste mainly composed of silver is applied thereon by screen
printing method, and a first internal electrode 141 is formed.
After laminating zinc oxide green sheets 10 of the same shape
thereon, a silver paste is applied by screen printing method, and a
second internal electrode 142 is formed. By repeating the same
process, a varistor 22 is formed.
[0046] On this varistor 22, zinc oxide green sheets 10 of the same
shape are laminated thereon, a silver paste is applied by screen
printing method, and a semicircular wiring conductor 12 is formed.
At a position connecting electrically with one end of the wiring
conductor 12, a zinc oxide green sheet 10 having a via conductor 13
is laminated. This via conductor 13 is formed by filling a via (not
shown) provided in the zinc oxide green sheet 10 with a silver
paste. Further, on this zinc oxide green sheet 10, a silver paste
is applied by screen printing method, and the remaining
semicircular wiring conductor 12 is formed. By repeating the same
process hereinafter, an inductor 21 as shown in FIG. 2 is formed.
Several zinc oxide green sheets 10 of same shape are laminated
thereon, and an upper side cover layer 232 is formed, and thus a
laminated body block is fabricated.
[0047] The thickness of the first internal electrode 141, second
internal electrode 142, and wiring conductor 12 is about 2.5 .mu.m.
In the actual process, a plurality of the shape as shown in FIG. 2
are fabricated at the same time, and the laminated body block is
cut into individual green chips, and by heating in the atmosphere
and removing the binder, they are heated and sintered at
930.degree. C. in the atmosphere.
[0048] By processing the ends of the sinter, the first internal
electrode 141, second internal electrode 142, and ends 121, 122 of
the wiring conductor 12 are exposed at the ends. Further, at the
shorter sides and longer sides of the ceramic sinter 25, a
conductor paste mainly composed of silver is applied and baked at
800.degree. C., and an external electrode for input 301, an
external electrode for output 302, and an external electrode for
grounding 31 are formed. Finally, by plating and forming a
laminated layer film of nickel and solder, the protection component
in the exemplary embodiment as shown in FIG. 1 is fabricated.
[0049] The obtained protection component of the exemplary
embodiment measures 1.6 mm in the longitudinal direction, 0.8 mm in
the lateral direction, and 0.8 mm in the thickness direction. The
capacitance between the external electrode for input 301 and
external electrode for grounding 31 is 75 pF, and the varistor
voltage V (1 mA), that is, the voltage when a current of 1 mA flows
is V=27 V. Incidentally, the inductance can be changed freely by
varying the length of the coil conductor 11 by adjusting the number
of layers when fabricating the inductor 21. In this exemplary
embodiment, two samples are prepared, having the inductance between
the external electrode for input 301 and external electrode for
output 302 of 68 nH and 220 nH.
[0050] In these two samples, the impedance frequency
characteristics were measured in the inductor 21, that is, between
the external electrode for input 301 and external electrode for
output 302. Results are shown in FIG. 4. As shown in FIG. 4, in a
frequency band of measuring frequency ranging from 300 MHz to 800
MHz, the impedance of the sample of which inductance is 68 nH is
200 .OMEGA. or less. In the sample with inductance of 220 nH, it is
200 .OMEGA. or more in all band.
[0051] Next, an electrostatic discharge test was conducted. FIG. 5
shows a circuit block diagram for the electrostatic discharge test.
By connecting a switch 103, a specified voltage is applied from a
direct-current power source 101 by way of resistor 102, and a
capacity box 104 of capacitance of 150 pF is charged with an
electric charge. By releasing the switch 103 and connecting a
switch 105, the electric charge accumulated in the capacity box 104
is applied as electrostatic discharge pulse to a protected
appliance 110 by way of resistor 106 and signal line 108.
[0052] As shown in FIG. 5, the protection component of the
exemplary embodiment is connected as an evaluation sample 109. That
is, the external electrode for input 203 is connected to the input
side of the signal line 108, that is, the resistor 106 side, the
external electrode for output 204 is connected to the output side
of the signal line 108, that is, to the protected appliance 110
side, and the external electrode for grounding 205 is connected to
the ground line 107. In this connection configuration, the inductor
202 is connected in series to the signal line 108 connected to the
protected appliance 110, and the varistor 201 is connected between
the input side of the signal line 108 and the ground line 107. In
this circuit configuration, by applying an electrostatic discharge
pulse, the voltage waveform was measured between the signal line
108 immediately before the protected appliance 110 and the ground
line 107. By this measurement, it was attempted to evaluate the
effect of suppressing the voltage applied to the protected
appliance 110 by bypassing the electrostatic discharge pulse, that
is, the absorption suppressing effect of the electrostatic
discharge pulse of the protection component of the evaluation
sample 109.
[0053] By way of comparison, a conventional laminated varistor of
which capacitance is 75 pF and varistor voltage V (1 mA) is 27 V
connected between the signal line 108 and ground line 107, and the
absorption suppressing effect of the electrostatic discharge pulse
is evaluated. The performance is also measured in the absence of
the laminated varistor or the protection component of the exemplary
embodiment.
[0054] Voltage waveforms of evaluation results are shown in FIG. 6,
FIG. 7, FIG. 8, and FIG. 9. In these diagrams, the axis of
abscissas denotes the time and the axis of ordinates represents the
measured voltage. FIG. 6 shows the voltage waveform when the
protection component is not provided, that is, when 8 kV is applied
as electrostatic discharge pulse in the absence of evaluation
sample 109 in the electrostatic discharge testing circuit in FIG.
5.
[0055] FIG. 7 shows the voltage waveform applied to the protected
appliance 110 when the conventional laminated varistor is connected
between the signal line 108 and ground line 107.
[0056] FIG. 8 shows the voltage waveform applied to the protected
appliance 110 when the protection component of the exemplary
embodiment of which inductance is 68 nH is disposed. FIG. 9 shows
the voltage waveform applied to the protected appliance 110 when
the protection component of the exemplary embodiment of which
inductance is 220 nH is disposed.
[0057] As clear from evaluation results in FIG. 7, FIG. 8 and FIG.
9, when using the conventional laminated varistor in FIG. 7, the
peak voltage is 155 V . By contrast, in the case of the protection
component of the exemplary embodiment, although the capacitance and
varistor voltage V (1 mA) of the varistor 22 are the same, the peak
voltage is 75 V in FIG. 8 and the peak voltage is 65V in FIG. 9,
and an outstanding voltage suppressing effect is recognized.
[0058] That is, when the protection component of the exemplary
embodiment is disposed, the varistor is connected to the signal
line input side and ground line, and the inductor is connected to
the signal line in series. As a result, the inductor connected in
series to the signal line becomes relatively high in impedance to
the high frequency component in the leading section of the
electrostatic discharge pulse, and passing of electrostatic
discharge pulse to the signal line is suppressed, and the varistor
characteristic becomes dominant, and the electrostatic discharge
pulse can be bypassed to the ground side in a short time by the
varistor, so that the voltage applied to the protected appliance
can be substantially decreased.
[0059] As clear from comparison of waveforms between FIG. 8 and
FIG. 9, the inductor 21 of the protection component of the
exemplary embodiment has a particularly excellent absorption
suppressing effect on the electrostatic discharge pulse when the
impedance is 200 .OMEGA. or more in a frequency band of measuring
frequency of 300 MHz to 800 MHz. More specifically, in the voltage
waveform in FIG. 8, that is, in the frequency band of measuring
frequency of 300 MHz to 800 MHz, in the case of protection
component with the impedance of 200 .OMEGA. or less and the
inductance of 68 nH, the voltage waveform applied to the protected
appliance 110 has a peak voltage of about 75 V in the leading time
of about 0.5 to 2 nanoseconds. By contrast, in the voltage waveform
in FIG. 9, that is, in all frequency band of measuring frequency of
300 MHz to 800 MHz, in the case of protection component with the
impedance of 200 .OMEGA. or more and the inductance of 220 nH, the
voltage waveform applied to the protected appliance 110 has no peak
voltage in the leading time of about 0.5 to 2 nanoseconds, and the
peak voltage itself is as small as about 65 V. That is, the
protection component of the exemplary embodiment has an outstanding
absorption suppressing effect on high frequency components in the
leading section of the electrostatic discharge pulse when the
impedance of the inductor 21 is 200 .OMEGA. or more in the
frequency band of measuring frequency of 300 MHz to 800 MHz, so
that the voltage applied to the protected appliance can be
lowered.
SECOND EXEMPLARY EMBODIMENT
[0060] FIG. 10 is a schematic perspective exploded view of ceramic
sinter 40 for composing a protection component in exemplary
embodiment 2 of the invention. FIG. 11 is an equivalent circuit
diagram of this protection component. What the protection component
of this exemplary embodiment differs from the protection component
in exemplary embodiment 1 lies in the structure of the ceramic
sinter. That is, in this exemplary embodiment, it is characteristic
that the ceramic sinter has one inductor and two varistors. The
outline shape of the protection component of the exemplary
embodiment is same as exemplary embodiment 1 shown in FIG. 1, and
FIG. 1 is cited as required. Same constituent components are
identified with same reference numerals.
[0061] A ceramic sinter 40 composing the protection component of
the exemplary embodiment is an integrated laminated body of first
varistor 221, second varistor 222, inductor 21, and cover layers
231, 232 as surface protective layers.
[0062] The inductor 21 includes a wiring conductor 12 formed in a
ceramic layer 10, and a via conductor 13 filling up a via (not
shown) opened in the ceramic layer 10, which are connected together
to form a spiral coil conductor 11. Ends 121, 122 of the coil
conductor 11 are drawn out to both shorter sides of the ceramic
sinter 25. This is same as in the ceramic sinter 25 in exemplary
embodiment 1, and in FIG. 10, the wiring conductor 12 is formed on
seven ceramic layers 10, and connected by the via conductor 13
formed in six vias, and the coil conductor 11 of 3.5 turns is
formed.
[0063] The first varistor 221 is formed by laminating the ceramic
layer 10, and first internal electrode 143 and second internal
electrode 144 different in shape formed on the ceramic layer 10
alternately, and the end of the first internal electrode 143 is
drawn out to the shorter side of the ceramic sinter 40, and the end
of the second internal electrode 144 is drawn out to this shorter
side and both longer sides in the vertical direction.
[0064] The second varistor 222 is also formed by laminating the
ceramic layer 10, and first internal electrode 145 and second
internal electrode 146 formed on the ceramic layer 10 alternately,
and the first internal electrode 145 is drawn out to the other
shorter side of the ceramic sinter 40, and the end of the second
internal electrode 146 is drawn out to this shorter side and both
longer sides in the vertical direction.
[0065] As known from the diagram, the end of the first internal
electrode 143 of the first varistor 221 and the end of the first
internal electrode 145 of the second varistor 222 are drawn out to
mutually different shorter sides. On the other hand, the second
internal electrode 144 of the first varistor 221 and the second
internal electrode 146 of the second varistor 222 are both drawn
out to both longer sides.
[0066] Further, as shown in the drawing, the first varistor 221 and
second varistor 222 are formed to enclose the inductor 21. In this
structure shown in FIG. 10, the inductor 21 is formed by laminating
seven ceramic layers 10 and the first varistor 221 and second
varistor 222 are formed by laminating three ceramic layers 10
respectively, but it is only shown schematically, and the number of
layers may be varied freely depending on the required inductance
value or capacitance value.
[0067] At one shorter side of the ceramic sinter 40 having such
internal structure, the external electrode for input 301
electrically connected to one end 122 of the coil conductor 11 and
the end of the first internal electrode 143 of the first varistor
221 is formed. At other shorter side of the ceramic sinter 40, the
external electrode for output 302 electrically connected to other
end 121 of the coil conductor 11 and the first internal electrode
145 of the second varistor 222 is formed. Further, in the middle of
both longer sides of the ceramic sinter 40, the external electrode
for grounding 31 electrically connected to the second internal
electrode 144 of the first varistor 221 and the second internal
electrode 146 of the second varistor 222 is formed. Thus, the
external electrode for input 301, external electrode for output
302, and external electrode for grounding 31 are formed ion the
ceramic sinter 40, and the protection component of the exemplary
embodiment is composed. Therefore, the outline configuration of the
protection component of the exemplary embodiment is same as that of
the protection component of exemplary embodiment 1 shown in FIG.
1.
[0068] However, the protection component of the exemplary
embodiment is an integral structure of one inductor 21 and two
varistors, that is, first varistor 221 and second varistor 222,
formed integrally in the ceramic sinter 40. The inductor 21 is
connected to the external electrode for input 301 and the external
electrode for output 302, electrically, the first varistor 221 is
connected to the external electrode for input 301 and the external
electrode for grounding 31, electrically, and the second varistor
222 is connected to the external electrode for output 302 and the
external electrode for grounding 31, electrically,
[0069] In this exemplary embodiment, on the basis of the shape
shown in FIG. 1, the region of forming the external electrode for
input 301 and external electrode for output 302 forms shorter
sides, but these external electrodes may not be always formed at
the shorter sides. That is, depending on the internal structure,
the external electrode for input 301 and external electrode for
output 302 may be formed at the longer sides, and the external
electrodes for grounding 31 may be formed at the shorter sides.
[0070] FIG. 11 is an equivalent circuit diagram of the protection
component of the exemplary embodiment. In FIG. 11, a first varistor
2011 and a second varistor 2012 correspond respectively to the
first varistor 221 and second varistor 222. An inductor 202
corresponds to the inductor 21. Similarly, the external electrode
for input 301, external electrode for output 302, and external
electrode for grounding 31 in FIG. 1 respectively correspond to an
external electrode for input 203, an external electrode for output
204, and an external electrode for grounding 205 in FIG. 11.
[0071] As known from the equivalent circuit in FIG. 11, in the
protection component of the exemplary embodiment, the first
varistor 2011 and second varistor 2012 are disposed parallel so as
to connect the both end of the inductor 202 and the external
electrode for grounding 205.
[0072] The manufacturing method of the protection component of the
exemplary embodiment is nearly same as the manufacturing method
shown in exemplary embodiment 1, and detailed description is
omitted. In this exemplary embodiment, however, after forming the
first varistor 221 and inductor 21, by repeating the process of
laminating further the ceramic layers 10, forming the second
internal electrode 146, laminating the ceramic layer 10 again, and
forming the first internal electrode 145, the process of forming
the second varistor 222 is added. After this process, a cover layer
232 is formed, and a laminated body block is fabricated. The
laminated body block is cut and sintered in the same process in
exemplary embodiment 1, and electrodes are formed, and the
protection component of this exemplary embodiment is manufactured.
In this exemplary embodiment, too, the ceramic layer 10 a zinc
oxide sheet obtained by sintering zinc oxide green sheet.
[0073] The obtained protection component of the exemplary
embodiment measures 1.6 mm in the longitudinal direction, 0.8 mm in
the lateral direction, and 0.8 mm in the thickness direction. The
capacitance between the external electrode for input 301 and
external electrode for grounding 31 is 75 pF, and the varistor
voltage V (1 mA) is V=27 V, and the capacitance between the
external electrode for output 302 and external electrode for
grounding 31 is 75 pF, and the varistor voltage V (1 mA) is V=27 V.
The inductance between the external electrode for input 301 and
external electrode for output 302 is 220 nH. Its impedance was 200
.OMEGA. or more in a frequency band of measuring frequency of 300
MHz to 800 MHz, same as the sample of inductance of 220 nH in the
protection component in exemplary embodiment 1 shown in FIG. 4.
[0074] In the protection component of the exemplary embodiment, the
suppressing effect on electrostatic discharge pulse was evaluated.
The method of evaluation is same as in exemplary embodiment 1, and
the protection component of the exemplary embodiment is used as the
evaluation sample 109 shown in FIG. 5. That is, in this exemplary
embodiment, too, the external electrode for input 203 is connected
to the input side of the signal line 108, that is, the resistor 106
side, the external electrode for output 204 is connected to the
output side of the signal line 108, that is, to the protected
appliance 110 side, and the external electrode for grounding 205 is
connected to the ground line 107. In this connection configuration,
8 kV of electrostatic discharge pulse applied from the circuit
shown in FIG. 5 was applied, and the voltage waveform applied to
the protected appliance 110 was measured, and the suppressing
effect was evaluated. Results of evaluation are shown in FIG.
12.
[0075] As shown in FIG. 12, when the protection component of the
exemplary embodiment was disposed, the peak voltage of the voltage
waveform applied to the protected appliance 110 was 65 V, and a
large voltage suppressing effect was confirmed. Contrary to this
configuration, by connecting the external electrode for input 203
of the protection component of the exemplary embodiment to the
output side of the signal line 108, that is, the protected
appliance 110 side, connecting the external electrode for output
204 to the input side of the signal line 108, that is, to the
resistor 106 side, and connecting the external electrode for
grounding 205 to the ground line 107, a similar electrostatic
discharge test was conducted. In this case, too, 8 kV of
electrostatic discharge pulse applied from the circuit shown in
FIG. 5 was applied, and the voltage waveform applied to the
protected appliance 110 was measured. As a result, also in this
configuration, the peak voltage of the voltage waveform applied to
the protected appliance 110 was 65 V, and a substantial voltage
suppressing effect was obtained.
[0076] By way of comparison, of the same protection component in
exemplary embodiment 1, a sample of which inductance is 220 nH was
measured by connecting reversely to the connection configuration of
the electrostatic discharge test in the case of exemplary
embodiment 1. That is, the external electrode for input 203 of this
sample is connected to the output side of the signal line 108, that
is, the protected appliance 110 side, the external electrode for
output 204 is connected to the input side of the signal line 108,
that is, to the resistor 106 side, and the external electrode for
grounding 205 is connected to the ground line 107. In this
constitution, 8 kV of electrostatic discharge pulse applied from
the circuit shown in FIG. 5 was applied, and the voltage waveform
applied to the protected appliance 110 was measured and evaluated.
Results are shown in FIG. 13.
[0077] As shown in FIG. 13, when connected reversely by using this
sample, the peak voltage of the voltage waveform applied to the
protected appliance 110 is 180 V, and the voltage suppressing
effect is lowered as compared with the connection configuration
shown in FIG. 9.
[0078] However, as clear from the equivalent circuit diagram and
electrostatic discharge test results in FIG. 11, the protection
component of the exemplary embodiment has same effects on both
input side and output side, and when electrostatic discharge is
carried out from either side, it is known that the voltage
suppressing effects as shown in FIG. 12 are obtained. Hence, by
using the protection component of the exemplary embodiment, it is
not required to check the direction of the component in the
mounting process, and the assembling process of electronic
appliance can be simplified outstandingly.
THIRD EXEMPLARY EMBODIMENT
[0079] A protection component in exemplary embodiment 3 of the
invention is described specifically below while referring to the
drawings. FIG. 14 is a schematic perspective exploded view of
ceramic sinter 50 for composing a protection component in this
exemplary embodiment. FIG. 15 is an equivalent circuit diagram of
this protection component.
[0080] What the protection component of this exemplary embodiment
differs from the protection component in exemplary embodiment 1 and
exemplary embodiment 2 lies in the structure of the ceramic sinter.
That is, in this exemplary embodiment, it is characteristic that
the ceramic sinter has two inductors and three varistors. The
outline shape of the protection component of the exemplary
embodiment is same as exemplary embodiment 1 and exemplary
embodiment 2, and FIG. 1 is cited when describing the outline
structure. Same constituent components as in exemplary embodiment 1
and exemplary embodiment 2 are identified with same reference
numerals.
[0081] A ceramic sinter 50 composing the protection component of
the exemplary embodiment is an integrated laminated body of cover
layers 231, 232, first inductor 211, second inductor 212, first
varistor 221, second varistor 222, and third varistor 223.
[0082] The cover layers 231, 232, first varistor 221, and second
varistor 222 are composed same as in the ceramic sinter 40 in
exemplary embodiment 2. It is a feature of this exemplary
embodiment that the third varistor 223 is formed between the first
inductor 211 and second inductor 212. This configuration is mainly
described below.
[0083] The first inductor 211 is formed on the first varistor 221.
The spiral coil conductor 111 is formed by connecting the wiring
conductor 123 formed on the ceramic layer 10 by the via conductor
133 filling the via (not shown) of the ceramic layer 10. In FIG.
14, this spiral coil conductor 111 has about 1.5 turns. One end
1231 of the coil conductor 111 is drawn to one shorter side of the
ceramic sinter 50. Other end of the coil conductor 111 is connected
to the middle of the first internal electrode 147 of the third
varistor 223 by means of the via conductor 136.
[0084] The third varistor 223 is formed on the first inductor 211.
This third varistor 223 is formed by alternately laminating the
first internal electrode 147 and second internal electrode 148 on
the ceramic layer 10. The first internal electrodes 147 are
mutually connected in the ceramic sinter 50 by means of the via
conductor 135. The third varistor 223 is also connected to the
wiring conductor 124 of the coil conductor 112 by means of the via
conductor 136 provided in the middle of the internal electrode 147
formed in the upper layer side ceramic layer 10. Both ends of the
second internal electrode 148 are drawn out to both longer sides of
the ceramic sinter 50. In FIG. 14, the third varistor 223 is formed
by laminating three layers of ceramic layer 10.
[0085] In the second inductor 212, similarly, the spiral coil
conductor 112 is formed inside the ceramic sinter 50. That is, the
wiring conductor 124 is formed on the ceramic layer 10, and the
wiring conductors 124 are mutually connected by the via conductor
134, and a second inductor 212 of about 1 turn is formed. One end
1241 of the coil conductor 112 is drawn out to the shorter side of
the ceramic sinter 50. Other end is connected to the middle of the
first internal electrode 147 of the third varistor 223 by means of
the via conductor 136 as mentioned above.
[0086] The second varistor 222 is formed on the second inductor
212.
[0087] In the first varistor 221, the ceramic layer 10 and first
internal electrodes 143 and second internal electrodes 144 are
laminated alternately. The first internal electrode 143 is formed
by shifting slightly to one end of the ceramic layer 10, and the
ends of the second internal electrode 144 are drawn out to both
longer sides. In the second varistor 222, too, the ceramic layer 10
and first internal electrodes 145 and second internal electrodes
146 are laminated alternately. The first internal electrode 145 is
formed by shifting slightly to one end of the ceramic layer 10, and
the ends of the second internal electrode 146 are drawn out to both
longer sides.
[0088] After laminating in this structure, it is cut, sintered and
processed in the same manufacturing method as shown in exemplary
embodiment 1. Later, external electrodes are formed on the ceramic
sinter 50. That is, at one shorter side of the ceramic sinter 50,
an external electrode for input 301 is formed for electrically
connecting to one end 1231 of the coil conductor 111 composing the
first inductor 211 and to the first internal electrode 143 of the
first varistor 221. At other shorter side of the ceramic sinter 50,
an external electrode for output 302 is formed for electrically
connecting to one end 1241 of the coil conductor 112 composing the
second inductor 212 and to the first internal electrode 145 of the
second varistor 222. At both longer sides of the ceramic sinter 50,
external electrodes for grounding 31 are formed for electrically
connecting to the ends of the second internal electrode 144 of the
first varistor 221, second internal electrode 146 of the second
varistor 222, and second internal electrode 148 of the third
varistor 223.
[0089] Thus, the protection component same in shape and appearance
as in exemplary embodiment 1 in FIG. 1 is obtained. In this
exemplary embodiment, the first varistor 221, second varistor 222,
and third varistor 223 are formed by laminating three ceramic
layers 10 each, but the number of layers is not particularly
specified. As many layers as required in design can be laminated.
Similarly, the first inductor 211 and second inductor 212 are
composed to have about 1 turn in the exemplary embodiment, but the
number of turns may be increasing by laminating more layers.
[0090] In this exemplary embodiment, too, the ceramic layer 10 is a
zinc oxide sheet obtained by sintering zinc oxide green sheet.
[0091] As described herein, the protection component of the
exemplary embodiment is an integral sintered structure of two
inductors 211, 212 and three varistors 221, 222, 223. The first
inductor 211 and second inductor 212 are electrically connected in
series, and are electrically connected to the external electrode
for input 301 and external electrode for output 302. The first
varistor 221 is electrically connected to the external electrode
for input 301 and external electrode for grounding 31. The second
varistor 222 is electrically connected to the external electrode
for output 302 and external electrode for grounding 31. The third
varistor 223 is electrically connected to the first inductor 211
and second inductor 212 at one side, and to the external electrode
for grounding 31 at other side.
[0092] In this exemplary embodiment, on the basis of the shape
shown in FIG. 1, the region of forming the external electrode for
input 301 and external electrode for output 302 forms shorter
sides, but these external electrodes may not be always formed at
the shorter sides. That is, depending on the internal structure,
the external electrode for input 301 and external electrode for
output 302 may be formed at the longer sides, and the external
electrodes for grounding 31 may be formed at the shorter sides.
[0093] A circuit configuration of this protection component is
shown in an equivalent circuit diagram in FIG. 15. In FIG. 15, a
first varistor 2011, a second varistor 2012, a third varistor 2013,
a first inductor 2021, and a second inductor 2022 correspond
respectively to the first varistor 221, second varistor 222, third
varistor 223, first inductor 211, and second inductor 212 of the
protection component. Similarly, an external electrode for input
203, an external electrode for output 204, and an external
electrode for grounding 205 correspond respectively to the external
electrode for input 301, external electrode for output 302, and
external electrode for grounding 31 of the protection
component.
[0094] The obtained protection component of the exemplary
embodiment measures 1.6 mm in the longitudinal direction, 0.8 mm in
the lateral direction, and 0.8 mm in the thickness direction. The
capacitance between the external electrode for input 301 and
external electrode for grounding 31 is 75 pF, and the varistor
voltage V (1 mA) is 27 V, and the capacitance between the external
electrode for output 302 and external electrode for grounding 31 is
75 pF, and the varistor voltage V (1 mA) is 27 V. The inductance
between the external electrode for input 301 and external electrode
for output 302 is 68 nH. Its impedance was 200 .OMEGA. or less in a
frequency band of measuring frequency of 300 MHz to 800 MHz, same
as the sample of inductance of 68 nH in the protection component in
exemplary embodiment 1 shown in FIG. 4.
[0095] In the protection component of the exemplary embodiment, the
suppressing effect on electrostatic discharge pulse was evaluated.
The method of evaluation is same as in exemplary embodiment 1, and
the protection component of the exemplary embodiment is used as the
evaluation sample 109 shown in FIG. 5. That is, in the protection
component of this exemplary embodiment, the external electrode for
input 301 is connected to the input side of the signal line 108
shown in FIG. 5, that is, to the resistor 106 side, the external
electrode for output 302 is connected to the output side of the
signal line 108, that is, to the protected appliance 110 side, and
the external electrode for grounding 31 is connected to the ground
line 107. In this connection configuration, later, 8 kV of
electrostatic discharge pulse applied from the circuit shown in
FIG. 5 was applied, and the voltage waveform applied to the
protected appliance 110 was measured, and the suppressing effect
was evaluated. Results of evaluation are shown in FIG. 16.
[0096] As shown in FIG. 16, when the protection component of the
exemplary embodiment was disposed, the peak voltage of the voltage
waveform applied to the protected appliance 110 was 65 V, and a
large voltage suppressing effect was confirmed.
[0097] In the protection component shown in FIG. 8, as compared
with the sample of which inductance of the inductor is 68 nH, the
peak value showing the suppressing effect was about 10 V lower. As
a result, the protection component of the exemplary embodiment was
known to have a substantial voltage suppressing effect of the
impedance value is low.
[0098] Also, as clear from the equivalent circuit diagram in FIG.
15, the protection component of the exemplary embodiment has same
effects on both input side and output side, and when electrostatic
discharge is carried out from either side, it is known that the
voltage suppressing effects as shown in FIG. 16 are obtained.
Hence, by using the protection component of the exemplary
embodiment, it is not required to check the direction of the
component in the mounting process, and the assembling process of
electronic appliance can be simplified outstandingly.
FOURTH EXEMPLARY EMBODIMENT
[0099] FIG. 17 is an outline perspective view of protection
component in exemplary embodiment 4 of the invention. FIG. 18 is a
schematic perspective exploded view of ceramic sinter 60 for
composing the protection component. FIG. 19 is an equivalent
circuit diagram of the protection component.
[0100] As shown in FIG. 17, the protection component of the
exemplary embodiment includes a first external electrode for input
402, a first external electrode for output 404, a second external
electrode for input 406, a second external electrode for output
408, and external electrodes for grounding 401, which are formed at
each end of a ceramic sinter 60. The first external electrode for
input 402 and first external electrode for output 404 form a pair,
and the second external electrode for input 406 and second external
electrode for output 408 form a pair.
[0101] As clear from the schematic perspective exploded view of
ceramic sinter 60 in FIG. 18, the ceramic sinter 60 is an integral
laminated structure of cover layers 412, 413, 414, 415, first
inductor 416, second inductor 417, first varistor 418, and second
varistor 419.
[0102] The structure of the ceramic sinter 60 is described
below.
[0103] The first inductor 416 is formed by a spiral coil conductor
422 connecting a wiring conductor 423 formed on the ceramic layer
420 by a via conductor 424 filling the via (not shown) formed
nearly in the middle of the ceramic layer 420. One end 4231 and
other end 4232 of the wiring conductor 423 for composing the coil
conductor 422 are drawn out to the mutually opposite ends.
[0104] The second inductor 417 is similarly formed by a spiral coil
conductor 425 connecting a wiring conductor 426 formed on the
ceramic layer 420 by a via conductor 427 filling the via (not
shown) formed nearly in the middle of the ceramic layer 420. One
end 4261 and other end 4262 of the wiring conductor 426 for
composing the coil conductor 425 are drawn out to the mutually
opposite ends.
[0105] The ends 4231, 4232 of the wiring conductor 423 of the first
inductor 416 and the ends 4261, 4262 of the wiring conductor 426 of
the second inductor 417 are similar ends, but are drawn out to
different positions.
[0106] The first varistor 418 is formed by alternately laminating
the ceramic layer 421, first internal electrode 428, and second
internal electrode 430 as shown in the drawing. One end of the
first internal electrode 428 is drawn out to the same position at
the same end as the end 4231 of the wiring conductor 423 of the
first inductor 416. Both ends of the second internal electrode 430
are drawn out to the middle of the end in the vertical direction to
the above end.
[0107] The second varistor 419 is similarly formed by alternately
laminating the ceramic layer 421, third internal electrode 429, and
second internal electrode 430 as shown in the drawing. One end of
the third internal electrode 429 is drawn out to the same position
at the same end as the end 4261 of the wiring conductor 426 of the
second inductor 417. Both ends of the second internal electrode 430
are drawn out to the middle of the end in the direction orthogonal
to the above end.
[0108] As shown in the drawing, the first internal electrode 428
and third internal electrode 429 are formed on the same ceramic
layer 421, and the size is about 1/2 as compared with the second
internal electrode 430. The first internal electrode 428 and third
internal electrode 429 are electrically separated in shape.
[0109] After laminating in this structure, by cutting into
specified shape, sintering, processing the ends and exposing the
electrode surfaces, a ceramic sinter 60 is obtained.
[0110] The ceramic sinter 60 has external electrodes formed on the
ends. The first external electrode for input 402 is formed so as to
be connected electrically to one end 4231 of the wiring conductor
423 of the coil conductor 422 and the first internal electrode 428
of the first varistor 418. The second external electrode for input
406 is formed so as to be connected electrically to one end 4261 of
the wiring conductor 426 of the coil conductor 425 and the third
internal electrode 429 of the second varistor 419.
[0111] Further, the first external electrode for output 404 is
formed so as to be connected electrically to the other end 4232 of
the wiring conductor 423 of the coil conductor 422. The second
external electrode for output 408 is formed so as to be connected
electrically to the other end 4262 of the wiring conductor 426 of
the coil conductor 425. The external electrodes for grounding 410
are formed so as to be connected electrically to the both ends of
the second internal electrode 430 common to the first varistor 418
and second varistor 419. Thus, the external electrodes are shown in
FIG. 17 are formed. As known from FIG. 17, these external
electrodes are individually separated electrically.
[0112] In the protection component of the exemplary embodiment, as
described herein, two inductors and two varistors are integrally
fabricated in the ceramic sinter 60. That is, an equivalent circuit
as shown in FIG. 19 is realized. The relation between this
equivalent circuit and the protection component of the exemplary
embodiment is described below. In FIG. 19, the first varistor 2011
and second varistor 2012 correspond to the first varistor 418 and
second varistor 419 of the protection component. The first inductor
2021 and second inductor 2022 correspond to the first inductor 416
and second inductor 417 respectively. The first external electrode
for input 2031, second external electrode for input 2032, first
external electrode for output 2041, second external electrode for
output 2042, and external electrodes for grounding 205 correspond
to the first external electrode for input 402, second external
electrode for input 406, first external electrode for output 404,
second external electrode for output 408, and external electrodes
for grounding 410, respectively.
[0113] Since the coil conductor 422 of the first inductor 416 and
the coil conductor 425 of the second inductor 417 are close to each
other, they are equivalently coupled electrically by way of a
capacitive component 206.
[0114] As explained herein, the protection component of the
exemplary embodiment comprises two lines of circuit configuration
in which the inductor is connected electrically to the external
electrode for input and external electrode for output, and the
varistor is connected electrically to the external electrode for
input and external electrode for grounding.
[0115] A manufacturing method of the protection component in the
exemplary embodiment is explained below while referring to FIG. 17
and FIG. 18.
[0116] First of all, two sheets are prepared, which are used as
ceramic layers 420, 421 after sintering. These are ferrite green
sheet comprising ceramic powder mainly composed of ferrite and an
organic binder, and zinc oxide green sheets comprising ceramic
powder mainly composed of zinc oxide and an organic binder. The
thickness of each green sheet is about 50 .mu.m. After sintering,
they are formed as a ceramic layer 420 of ferrite sheet and a
ceramic layer 421 of zinc oxide sheet, but they are not
distinguished before and after sintering in the following
explanation, and are respectively called ferrite green sheet 420
and zinc oxide green sheet 421.
[0117] Consequently, a plurality of ferrite green sheets 420 are
laminated, and a lower side cover layer 412 is formed. In
succession, a conductor paste mainly composed of silver is applied
on the cover layer 412, and a conductor wiring 423 is formed by
screen printing method. Further on the wiring conductor 423, a
ferrite green sheet 420 forming a via conductor 424 filled with
silver paste is laminated at a position to be connected
electrically. After lamination, silver paste is further applied,
and a wiring conductor 423 is formed by screen printing method. In
this process, a first inductor 416 is formed.
[0118] By repeating the same process, a wiring conductor 426 is
formed, and a second inductor 417 is formed. After forming the
second inductor 417, further, a plurality of ferrite green sheets
420 are laminated on this sheet, and an intermediate cover layer
413 is formed. As a result, the first inductor 416 composed of coil
conductor 422 and the second inductor 417 composed of coil
conductor 425 can be fabricated.
[0119] Further thereon, by laminating a plurality of zinc oxide
green sheets 421, an intermediate cover layer 414 is formed. In
succession, a conductor paste mainly composed of silver is applied
on the cover layer 414, and a first internal electrode 428 and a
third internal electrode 429 are formed on the same sheet by screen
printing method. Further after laminating the zinc oxide green
sheet 421 thereon, silver paste is applied, and a second internal
electrode 430 is formed by screen printing method. By repeating
this process several times, a first varistor 418 and a second
varistor 419 are formed.
[0120] By laminating a plurality of zinc oxide green sheets 421, an
upper side cover layer 415 is formed, and thus a laminated body
block is fabricated.
[0121] The thickness of each conductor layer is about 2.5 .mu.m. In
the lamination composition shown in FIG. 18, multiple pieces are
printed simultaneously so that the shape may be as shown in FIG. 18
after cutting.
[0122] By cutting at specified positions and separating the
laminated body block, individual green chips are formed. By heating
the green chips in the atmosphere and removing the binder, they are
heated and sintered at 930.degree. C. in the atmosphere, and a
sinter is obtained.
[0123] By processing the ends of the sinter, and exposing the
wiring conductors and internal electrodes formed in the sinter on
the surface, a ceramic sinter 60 is fabricated. A conductive paste
mainly composed of silver is applied to the ends of the ceramic
sinter 60, and by baking at 800.degree. C., a first external
electrode for input 402, a second external electrode for input 406,
a first external electrode for output 404, a second external
electrode for output 408, and an external electrodes for grounding
410 are formed, and further by plating with nickel or solder, the
protection component in the exemplary embodiment is fabricated.
[0124] The obtained protection component of the exemplary
embodiment measures 1.4 mm in the longitudinal direction, 1.0 mm in
the lateral direction, and 0.8 mm in the thickness direction. The
capacitance between the first external electrode for input 402 and
external electrode for grounding 410 is 75 pF, and the varistor
voltage V (1 mA) is 27 V. The impedance between the first external
electrode for input 402 and first external electrode for output 404
is as shown in FIG. 20. That is, it was 200 .OMEGA. or more in the
frequency band of measuring frequency of 300 MHz to 800 MHz. The
capacitance between the second external electrode for input 406 and
external electrode for grounding 410, the varistor voltage V, and
the impedance between the second external electrode for input 406
and second external electrode for output 408 were also similar as
mentioned above.
[0125] Next, an electrostatic discharge test was conducted in the
protection component of the exemplary embodiment manufactured in
this manner. The evaluation was same as the method of electrostatic
discharge test explained in exemplary embodiment 1. That is, the
protection component of the exemplary embodiment is the evaluation
sample 109 shown in FIG. 5, and the first external electrode for
input 2031 was connected to the input side of the signal line 108,
that is, to the resistor 106 side, the first external electrode for
output 2041 is connected to the output side of the signal line 108,
that is, to the protected appliance 110 side, and the external
electrode for grounding 205 is connected to the ground line 107. In
this connection configuration, later, 8 kV of electrostatic
discharge pulse applied from the circuit shown in FIG. 5 was
applied, and the voltage waveform applied to the protected
appliance 110 was measured, and the suppressing effect was
evaluated. Results of evaluation are shown in FIG. 21.
[0126] As shown in FIG. 21, when the protection component of the
exemplary embodiment was disposed, the peak voltage of the voltage
waveform applied to the protected appliance 110 was 60 V, and a
greater voltage suppressing effect was confirmed as compared with
exemplary embodiment 1, exemplary embodiment 2, or exemplary
embodiment 3.
[0127] Suppressing effects were similarly evaluated by connecting
the second external electrode for input 2032 to the input side of
the signal line 108, that is, to the resistor 106 side, the second
external electrode for output 2042 to the output side of the signal
line 108, that is, to the protected appliance 110 side, and the
external electrode for grounding 205 to the ground line 107, and
the same results as in FIG. 21 were obtained.
[0128] The protection component of the exemplary embodiment is
applicable to two lines by one system, and the number of parts and
mounting cost can be curtailed. Further, since the two inductors
enclosed by the ferrite sheet are mutually coupled capacitively, it
also as the function as common mode noise filter. For example, when
one protection component of exemplary embodiment 1 is provided in
each one of the two signal lines, the impedance at 100 MHz in the
common mode is several ohms to tens of ohms. By contrast, as in
this exemplary embodiment, when the protection component having two
lines is provided in two signal lines, the impedance at 100 MHz in
the common mode is 100 .OMEGA. or more. As a result, a great effect
as noise filter in the common mode is recognized.
[0129] In exemplary embodiment 1 to exemplary embodiment 4, the
varistor is disposed in the ceramic layer composed of zinc oxide
sheet, but it may be also disposed in a ceramic layer mainly
composed of strontium titanate. The inductor is provided in the
ceramic sheet composed of zinc oxide sheet in exemplary embodiment
1 to exemplary embodiment 3, and in the ceramic sheet composed of
ferrite sheet in exemplary embodiment 4, but it is also possible to
disposed in a ceramic sheet of low dielectric constant.
[0130] In exemplary embodiment 4, the ceramic sinter 60 is
fabricated by integrally sintering the varistor provided in the
ceramic sheet of zinc oxide sheet and the inductor provided in the
ceramic layer of ferrite sheet. However, the invention is not
limited to such configuration alone. For example, by individually
cutting and sintering, a ceramic sinter 60 may be composed by
adhering with an adhesive. By composing the ceramic sinter 60 in
such manner and forming external electrodes, an protection
component having similar performance can be realized. Within
allowable ranges of mechanical strength and dimensions, the number
of varistors or inductors may be increased to 4 or 8, for example,
and 4 or 8 lines may be formed.
[0131] The protection components in exemplary embodiment 1 to
exemplary embodiment 4 also have the function of low pass filter by
the inductance of inductor and capacitance of varistor, and
therefore by setting the inductance and capacitance at proper
values, a multi-stage low pass filter of L type or pi-type may be
realized, and the function as the low pass filter may be further
enhanced.
[0132] Further, the protection component of the invention as the
following features. That is, in the protection component of the
invention, when the inductor has the impedance of 200 .OMEGA. or
more in the frequency band of measuring frequency of 300 MHz to 800
MHz, peak voltage of about 0.5 to 2 nanoseconds of electrostatic
discharge pulse can be suppressed more securely, and the protective
effect of the electronic circuit of the appliance is more securely
assured.
[0133] In the case of n-type configuration connecting the inductor
in series to the signal line and the varistor parallel to the
inductor, a function of low pass filter (noise filter) of high
noise removing effect is realized by the inductance of the inductor
and capacitance of the varistor.
[0134] In a configuration comprising a plurality of inductors and a
plurality of varistors, by optimally setting the inductance of the
inductor and capacitance of the varistor, a function of a desired
multi-stage low pass filter (noise filter) maybe also realized.
[0135] Also in a configuration comprising a plurality of external
electrodes for input and external electrodes for output, the
inductors existing on different lines maybe electrically coupled
capacitively, and an element having a function of common mode choke
coil may be also realized.
* * * * *